{ diff(x1, t) = (1*k9*k1 + (-1)*k9*k2*x1*x2^k4/(k3^k4 + x2^k4))/k9,
  diff(x2, t) = (1*k9*k5*(1 - x2)*x1^k8/(k7^k8 + x1^k8) + (-1)*k9*k6*x2)/k9 }